The Mutisieae (Asteraceae) are a diverse basal lineage. A polymorphous paraphyletic group of about 50 South American species within the Mutisieae are characterized by having foliaceous outer involucral bracts and winged inner bracts. This publication presents the results of the systematic and taxonomic study of these taxa. The research focuses on newly assessed morphological and anatomical variation of characters taken from habit, involucral bracts, and achenes, combined with palynological and genetic (nr DNA) information. The genus Chaetanthera (30 species) is extensively revised and the genus Oriastrum (18 species) is reinstated. Character variation is considered in the light of form, function and habitat. Primary (cold) and secondary (aridity) adaptations to environmental conditions and trends towards insular syndromes are discussed. The biogeography of the species is explored. Three case studies of species complexes within Chaetanthera demonstrate the occurrence of polymorphism as evidence of active speciation and hybridisation events. Species keys and detailed descriptions are provided.